1. Field of the Invention
The present invention relates to camera modules and, more specifically, to a camera module in which a light-receiving element and an image pickup lens are unified by packaging.
2. Description of Related Art
In recent years, a cameral module, in which an imaging element and an image pickup lens are incorporated by being integrated with each other, is used as a camera system containing a signal processing system in an application of mounting to a compact information terminal such as a personal computer or a portable television telephone.
For example, a portable telephone equipped with a small camera takes a picture of a speaker so as to take it in as image data, and transmits the image data to a telephoning party. Such a small camera generally comprises a CMOS (or CCD) sensor as an imaging element and an image pickup lens.
Miniaturization of portable telephones and personal computers is advanced further, and further miniaturization is required for a small camera, which is incorporated into such equipments. In order to satisfy such a demand for the small camera, a camera module, which is formed by incorporating an image pickup lens and a CMOS (CCD) sensor into a single package, has been developed.
In the module, an optical filter is arranged between the lens and the imaging element for the purpose of improving image quality (flare, ghost, moiré fringes). As such an optical filter, an optical low-pass filter (OLPF) of a crystal plate formed with an anti-reflection film or an infrared cut filter film or a glass plate applied with an infrared cut film is used widely.
The camera module generally comprises a lens holder for holding an image pickup lens and a package for holding an imaging element. Since the above-mentioned optical filter is arranged between the image pickup lens and the imaging element, there are a case in which the optical filter is attached on the lens holder side and a case in which the optical filter is attached on the package side.
The optical filter is formed so as to function as a desired optical filter by forming a film on a large substrate, and thereafter, cut out as individual filters of a predetermined size. At this time, minute unevenness of an order of several micrometers or several tens micrometers. Additionally, cutting-burrs may be formed or minute particles of a cover film may be adhered on the optical filter. The optical filter after cutting is cleaned by air blow or the like since an optical filter function may be deteriorated if it is washed by water or liquid.
However, according to air blow, extraneous matter cannot be removed completely. For this reason, in the process of incorporating an optical filter into a camera module, when vibration or shock is applied to the optical filter, the above-mentioned burr or extraneous matter (hereinafter, referred to as minute particles) may be separated from the optical filter and remain in the camera module. Additionally, when a vibration or shock is applied to the camera module during use or transportation of equipments using the camera module, the above-mentioned minute particles may be separated from the optical filter.
Since the optical filter is arranged above the imaging element, the minute particles separated from the optical filter may fall onto an imaging surface of the imaging element. In such a case, there is a problem in that quality of the image obtained by the camera module is deteriorated.
Additionally, as a structure of the camera module, for example, there is suggested a structure in which an imaging element is attached to one surface of a plastic molded part and a lens holder having an image pickup lens is attached to an opposite side surface of the plastic molded part. A through hole for passing a light from the lens toward the imaging element is provided in the plastic molded part. The imaging element is flip-chip mounted to a wiring pattern formed on the one surface of the plastic molded part. The imaging element detects a light incident on an element surface in which a light-receiving part or a micro lens is present, and performs a photoelectric conversion. The thus-obtained electric image signal is supplied to a signal processing circuit or the like, and an image is displayed on a screen of a display based on the processed image signal.
In the cameral module of the above-mentioned structure, it is necessary to make a thickness of the plastic molded part (that is, a distance between the image pickup lens and the imaging element) to be a predetermined dimension so as to acquire a focal distance of the image pickup lens, and, thus, there exists a wasted space in the plastic molded part. Accordingly, there is a demand for effective use by embedding a component part in the wasted space in the plastic molded part.
Thus, there is suggested a structure in which a signal processor having the above mentioned signal processing circuit or the like formed therein is embedded in the plastic molded part. However, when the camera module operates, an electromagnetic filed is generated from the processor element incorporated in the package of the cameral module. There may be a problem generated due to influences of such an electromagnetic field in that a noise is generated in the image signal output from the imaging element, thereby deteriorating the image.
It should be noted that there are the following patent documents as documents relevant to the present invention.
1. Japanese Laid-Open Patent Application No. 2003-189195
2. Japanese Patent Publication No. 6-7587